Conventionally, there have been proposed electronically controlled throttle control apparatuses which have an opener side function of mechanically holding a throttle valve in a predetermined intermediate position between a fully-closed position and a fully-open position by utilizing respective different biasing forces of a plurality of springs when the supply of an electric current to a drive motor is interrupted for any reason, thereby preventing an internal combustion engine from entering a halt state immediately so that the vehicle can run for evacuation (see publication of U.S. Pat. No. 5,492,097, pp. 1–9, FIGS. 1–9).
Nevertheless, while the conventional electronically controlled throttle control apparatuses have had the opener side function of holding the throttle valve in the intermediate position when the supply of the electric current to the drive motor is interrupted for any reason, there have been the problems of a greater number of parts and an overall higher cost since two lever members including an opener member and an intermediate stopper member and two spring members including a spring for the opener side function and a spring for a return side function are necessary. In addition, since the intermediate stopper member to come into contact with a locking part on the throttle-body side adopts the complicated configuration that it sets the intermediate position of the throttle valve via the contacting portion with the opener member, there has been the problem that the opening position of the throttle valve at the intermediate position can vary even with such variations as part tolerances.
Then, in order to solve the foregoing problems, there has been proposed a single spring (coil spring 100) structure of coil form in which, as shown in FIGS. 12 to 15B, a coupling portion between a first spring part 101 having the return side function (hereinafter, referred to as return spring function) and a second spring part 102 having the opener side function (hereinafter, referred to as opener spring function) is bent into a generally inverted U-shape to form a U-shaped hook part 103 to be fixed to an intermediate position fixed to a throttle body 114, and both sides (one end of the first spring part 101 and the other end of the second spring part 102) are wound in different directions (see Japanese Patent Laid-Open Publication No. 2002-256894, pp. 1–10, FIGS. 1–7), with the objectives of reducing the parts count of the opener mechanism of the electronically controlled throttle control apparatus for a simplified configuration and improving the opening position accuracy of the throttle valve at the intermediate position (also referred to as default position). Incidentally, 121 designates a body-side hook, 122 a gear-side hook, 123 anti-sideslip guides, 124 an engaging part formed on an opener member 106, and 125 a spring inner periphery guide on the body side.
In the electronically controlled throttle control apparatus described in Japanese Patent Laid-Open Publication No. 2002-256894, when a throttle valve 104 and a throttle shaft 105 are closed from the intermediate position toward the fully-closed position, the U-shaped hook part 103 of the single coil spring 100 is locked by an intermediate stopper member 115. Additionally, the opener member 106 is integrally formed on an opposed surface of a valve gear 111 constituting a component of a power transmission device (for example, a geared reduction device composed of the valve gear 111, an intermediate reduction gear 112, and a pinion gear 113) and transmits rotational power of a drive motor 110 to the throttle valve 104. The throttle shaft 105 rotates with the other end of the second spring part 102, or a spring gear-side hook 107, to generate a biasing force in the direction of returning from the fully-closed position to the intermediate position while a spring inner periphery guide 108 for holding the inner side of the second spring part 102 of the single coil spring 100 makes a large relative movement with respect to the inner periphery of the second spring part 102.
The foregoing has thus yielded a new problem that when the throttle valve 104 and the throttle shaft 105 are closed from the default position toward the fully-closed position, the relative movement between the outer periphery of the spring inner periphery guide 108 integrally formed on the opposed surface of the valve gear 111 along with the opener member 106 and the inner periphery of the second spring part 102 of the single coil spring 100 can produce a large sliding resistance. This resistance can potentially cause a malfunction of the throttle valve 104 and the throttle shaft 105 and an increase in the rotational load of the drive motor 110.
In the electronically controlled throttle control apparatus described in the foregoing Japanese Patent Laid-Open Publication No. 2002-256894, when the throttle valve is closed from the intermediate position toward the fully-closed position, the U-shaped hook part of the coil spring is locked by the intermediate stopper member and the opener member rotates with an end of the second spring part, or a spring-gear-side hook, to produce a biasing force for returning from the fully-closed position to the intermediate position while the spring inner periphery guide for holding the inside of the coil spring makes a large relative movement with respect to the inner periphery of the second spring part of the coil spring.
Consequently, when the throttle valve is closed from the intermediate position toward the fully-closed position, there occur the problems that the relative movement between the outer periphery of the spring inner periphery guide and the inner periphery of the second spring part causes malfunction of the throttle valve, and that sliding friction between the outer periphery of the spring inner periphery guide and the inner periphery of the second spring part produces abrasive dust.
In particular, the abrasive dust may be rubbed firmly against the outer periphery of the spring inner periphery guide or the inner periphery of the second spring part by the sliding friction between the outer periphery of the spring inner periphery guide and the inner periphery of the second spring part. When the abrasive dust is thus rubbed against the surface of the spring inner periphery guide or the second spring part, the spring inner periphery guide or the second spring part gets warped at the surface, giving rise to the problem that the sliding resistance in the relative movement between the outer periphery of the spring inner periphery guide and the inner periphery of the second spring part, i.e., the sliding resistance ascribable to the intervention of the abrasive dust between the outer periphery of the spring inner periphery guide and the inner periphery of the second spring part is made even greater to promote further malfunction of the throttle valve.
Moreover, when the spring inner periphery guide is integrally formed on a valve gear which constitutes a component of a power transmission device (such as a reduction gear device) for transmitting the rotational power of the drive motor to the throttle shaft for holding and fixing the throttle valve, there occurs the problem that the power transmission device causes a malfunction if the foregoing abrasive dust is scattered into a gear case accommodating the power transmission device and adheres to the gear meshing part.